1. Field of the Invention
The present invention relates to a light source driving circuit for driving a light source, an optical scanning device that includes the light source driving circuit, and an image forming apparatus that includes the light source driving circuit.
2. Description of the Related Art
In an image forming apparatus according to related art, predetermined optical output is gained from a light source, such as a laser diode (LD), and density of an image is expressed by exposing a photoreceptor.
It is known that, until a predetermined level of optical output is achieved from a light source, a certain time period may be elapsed (i.e., an emission delay time may occur) depending on response characteristics of the light source. It is also known that, from the start of supplying a predetermined electric current to a light source until detection of a predetermined level of optical output, an emission delay time may occur that depends on a parasitic capacitance of a circuit in which a light source is implemented.
Consequently, for an image forming apparatus according to related art, for example, when a time period for outputting light is a short time period that is shorter than several nanoseconds, a rising edge of an optical output waveform may be rounded due to an effect of the emission delay time and so forth. Accordingly, a predetermined light amount may not be achieved within such a short time period. It is known that, similar to the case of the rising edge, a falling edge of the waveform may be rounded at a moment of stopping supply of a predetermined electric current to a light source. The rounding of the falling edge of the light output waveform may be caused by a time spent for electric potential of a light source to transition from electric potential corresponding to a state where the light source is turned on to electric potential corresponding to a state where the light source is turned off.
Many attempts have been made to overcome such a situation. For example, Patent Document 1 (Japanese Unexamined Patent Publication No. 2011-198877) discloses that an overshoot is provided during a time period of rising to a predetermined electric current level, and an undershoot is provided to a time period of falling. Further, Patent Document 2 (Japanese Patent No. 4476568) discloses that an overshoot electric current and/or undershoot electric current is adjusted depending on a bias current and a switching current.